On the phonon spectra of polysulphurnitride, (SN)x

Abstract

A four-parameter valence force model is presented on the basis of a simplified three-dimensional (SN)_x structure. It describes reasonably the gross features of the phonon data known up to now. Evidence for non-central interchain forces is found. The model favours a high-frequency cut-off of the optic spectra at 1004 cm^-1. Thus it further suggests that only two lines (1004 cm^-1, 660 cm^-1) out of all experimental A_g frequencies larger than 600 cm^-1 are associated with a first-order Raman process. It explains why the intensity of the peak at 660 cm^-1 is expected to be much stronger than that of the 1004 cm^-1 mode. The importance of internal strain effects in (SN)_x is manifested. The phonon dispersion curves calculated along (010) are presented.